In GSM (Global System for Mobile communications) systems, a mobile station (MS) consists of a wireless terminal (i.e., handset) and a removable smart card called a Subscriber Identity Module (SIM). In 3rd Generation (3G) Universal Mobile Telecommunication Systems (UMTSs), User Equipment (UE) consists of mobile equipment (ME) and a removable smart card called the UMTS Subscriber Identity Module (USIM). The ME communicates with a UMTS Terrestrial Radio Access Network (UTRAN) node, which in turn, may establish a connection to a Circuit Switched (CS) or Packet Switched (PS) Core network.
An International Mobile Equipment Identity (IMEI) uniquely identifies the mobile equipment. The SIM or USIM card contains an International Mobile Subscriber Identity (IMSI) which uniquely identifies the subscriber. The IMEI and the IMSI are independent, thereby allowing personal mobility.
In the case of 3G UMTSs, a base station controller corresponds to a radio network controller (RNC). There, a plurality of base stations are controlled by a node B, which in turn has a connection to the RNC.
The SIM or the USIM provides personal mobility so that a user can have access to subscribed services irrespective of a specific terminal. By inserting the SIM card into another GSM or 3G terminal, the user is able to receive calls, make calls and receive other subscribed services from that terminal.
FIG. 1 shows a conventional 3G UMTS 100 which includes a typical MS or UE 105 having a handset 110 with a respective USIM or SIM card 115 inserted therein. The USIM or SIM card 115 stores Public Land Mobile Network (PLMN) information and IMSI information. When a request to connect the MS 110 is received (by dialing or receiving a call) (S1), the PLMN and IMSI information is transferred from the USIM or SIM card 115 to the handset 110 for facilitating an initial cell search and to camp on the cell determined from the search (S2). A communication link between the MS or UE 105 and a UTRAN node 120 is established, and system information is sent from the UTRAN node 120 to the MS or UE 105 (S3A, S3B). In response, the MS or UE 105 sends a connection request including the stored IMSI information to the UTRAN node 120 (S4). Once the connection is granted by the UTRAN node 120 (S5A, S5B), the MS or UE 105 may be used to request a transfer and/or connection to a CS or PS Core network 125 (S6A, S6B). Once the MS or UE 105 is connected to the Core network 125 (S6B), data may be transferred between the Core network and the MS or UE 105 (S7).
Protocol enhancements, specified by 3GPP TS 23.003, allow transparent routing of IP datagrams to mobile nodes in the Internet. An IP datagram is the fundamental unit of information passed across any network utilizing the Internet protocol. An IP datagram contains source and destination addresses, along with data and a number of fields that define such things as the length of the datagram, the header checksum and flags that indicate whether the datagram can be (or has been) fragmented.
Each mobile node is always identified by its home address, regardless of its current point of attachment to the Internet. A mobile node is a host or router that changes its point of attachment from one network or sub-network to another. A mobile node may change its location without changing its IP address. Thus, a mobile node may continue to communicate with other Internet nodes at any location using its constant IP address, assuming link-layer connectivity to a point of attachment is available.
When located away from its home, a mobile node is also associated with a care-of address, which provides information about its current point of attachment to the Internet. The care-of address is the termination point of a tunnel toward a mobile node. A tunnel is the path followed by a datagram while it is encapsulated. A foreign agent care-of message is an address of a foreign agent with which the mobile node is registered. A co-located care-of message is an externally obtained local address which the mobile node has associated with one of its own network interfaces.
The protocol provides for registering the care-of address with a home agent. A home agent is a router on a mobile node's home network which tunnels data grams for delivery to the mobile node when it is away from home, and maintains current location information for the mobile node. The home agent sends data grams destined for the mobile node through a tunnel to the care-of address. After arriving at the end of the tunnel, each datagram is then delivered to the mobile node.
In Internet routing, a care-of address is a temporary IP address for a mobile node (mobile device) that enables message delivery when the device is connecting from somewhere other than its home network. The care-of address identifies a mobile node's current point of attachment to the Internet and makes it possible to connect from a different location without changing the device's home address (permanent IP address). This works similarly to the way the postal system might forward letters through a care-of address: messages sent to the known permanent address are rerouted to the care-of address while the recipient can be reached there. Thus, the recipient avoids having to change their official address to the temporary one when they change their location, and change it back again when they return home.
When a mobile device is away from its home network, it is assigned a care-of address. This may be a foreign agent care-of address, which is the static IP address of a foreign agent on a visited network, or a co-located care-of address, which is a temporary IP address assigned to the mobile node. A co-located care-of address may be acquired through some means such as Dynamic Host Configuration Protocol (DHCP), or may be a longer-term address assigned a device for connecting through a specific foreign network. Mobile IP, as defined in the Internet Engineering Task Force (IETF) RFC 2002 specifications, registers the care-of address with a home agent which resides on the home network. When a message for the mobile node is delivered to the home network, the home agent intercepts the message and tunnels it to the recipient at the care-of address.
UEs can only be operated if a valid IMSI is present. An IMSI is primarily intended for obtaining PLMN information by subscribers for individual charging purposes. Current cellular systems, however, do not address the use of an MS or UE in the context of an IP-based network. As the use of IP-based networks becomes ubiquitous, the lack of IP-enabled functionality will present a problem for many MS or UE users.